Mitochondria arose from aerobic prokaryotes: phagocytosed by eukaryotes. Mitochondria can divide within the cell: mitochondrial fission. Serves as the outer boundary of the organelle. Has a diverse number of proteins that function as enzymes. Porins: beta pleated sheets, can allow passage of large number of molecules, respond to conditions within the cell, intermembrane space. Gel-like consistency from the high concentration of proteins. Mitochondrial dna encodes ~ 37 genes in humans: two membranes, two aqueous compartments. The majority of proteins that function in the mitochondria are encoded by dna in the cell nucleus. These proteins are translated on free ribosomes in the cytosol. At the n-terminus of proteins composed of several positively charged residues: inner membrane mitochondrial proteins. Contain internal targeting sequences (poorly defined) and stop-transfer sequences: for mitochondrial import. Proteins need to be in an unfolded state. Unfolded proteins then bind to membrane receptors on outermitochondrial membrane. Receptors are located close to large protein channels called tom complexes.